In some regions of the world, the transportation of natural gas through pipelines is uneconomic. The natural gas is therefore cooled to a temperature below its boiling point, e.g. −160° C., until becoming liquid and the liquefied natural gas (LNG) is subsequently stored in tanks. Since the volume of natural gas is considerably less in liquid phase than in gaseous phase, the LNG can be conveniently and economically transported by ship to a destination port.
In the vicinity of the destination port, the LNG is transported to a regasification terminal, whereat it is reheated by heat exchange with sea water or with the exhaust gas of gas turbines and converted into gas. Each regasification terminal is usually connected with a distribution network of pipelines so that the regasified natural gas may be transmitted to an end user. While a regasification terminal is efficient in terms of the ability to vaporize the LNG so that it may be transmitted to end users, there is a need for an efficient method for harnessing the cold potential of the LNG as a cold sink for a condenser to generate power.
Use of Rankine cycles for power generation from evaporating LNG are considered in “Design of Rankine Cycles for power generation from evaporating LNG”, Maertens, J., International Journal of Refrigeration, 1986, Vol. 9, May. In addition, further power cycles using LNG/LPG (liquefied petroleum gas) are considered in U.S. Pat. No. 6,367,258. Another power cycle utilizing LNG is considered in U.S. Pat. No. 6,336,316. More power cycles using LNG are described in “Energy recovery on LNG import terminals ERoS RT project” by Snecma Moteurs, made available at the Gastech 2005, The 21st International Conference & Exhibition for the LNG, LPG and Natural Gas Industries,—14/17 Mar. 2005 Bilbao, Spain.
On the other hand, a power cycle including a combined cycle power plant and an organic Rankine cycle power plant using the condenser of the steam turbine as its heat source is disclosed in U.S. Pat. No. 5,687,570, the disclosure of which is hereby included by reference.
It is an object of the present invention to provide an LNG-based power and regasification system, which utilizes the low temperature of the LNG as a cold sink for the condenser of the power system in order to generate electricity or produce power for direct use.
Other objects and advantages of the invention will become apparent as the description proceeds.